Systems and methods for guiding a medical instrument through a body

ABSTRACT

Guidance systems for guiding a catheter through tissue within a body are described. In one form, the system is implemented in connection with a catheter which includes a catheter body having a optic fibers extending between a first end and a second end thereof. The guidance system is coupled to the catheter body and includes a first optic fiber, a second optic fiber, and a detecting element. The first optic fiber includes a first end and a second end, and is coupled to the catheter body so that the first optic fiber second end is adjacent the catheter second end. The second optic fiber also includes a first end and a second end, and a reference mirror is positioned adjacent the second optic fiber second end. The first optic fiber first end is communicatively coupled to the detecting element and the second optic fiber first end is communicatively coupled to the detecting element. The detecting element is configured to determine interference between a light beam propagating through the first optic fiber and a light beam propagating through the second optic fiber.

FIELD OF THE INVENTION

[0001] This invention relates generally to medical instruments and, moreparticularly, to systems and methods for guiding medical instrumentsthrough a body or a portion of the body, such as a blood vessel.

BACKGROUND OF THE INVENTION

[0002] Disease processes, e.g., tumors, inflammation of lymph nodes, andplaque build-up in arteries, often afflict the human body. To treat suchdisease, it often is necessary to insert a medical device into the body,and to guide the medical device to the diseased site. Once the medicaldevice is adjacent the diseased site, the medical device typically isused to photoablate or otherwise remove or reduce the diseased tissue.

[0003] As one specific example, atherosclerotic plaque is known tobuild-up on the walls of arteries in the human body. Such plaquebuild-up restricts circulation and often causes cardiovascular problems,especially when the build-up occurs in coronary arteries. Accordingly,it is desirable to detect plaque build-up and remove or otherwise reducesuch plaque build-up.

[0004] Known catheters implement laser energy to remove plaque build upon artery walls. One known catheter includes a laser source and acatheter body. The catheter body has a first end and a second end, orhead, and several optical fibers extend between the first end and thesecond end. The laser source is coupled to each of the optical fibersadjacent the catheter body first end and is configured to transmit laserenergy simultaneously through the optical fibers.

[0005] To remove arterial plaque, for example, the catheter body ispositioned in the artery so that the second end of the catheter body isadjacent a region of plaque build-up. The laser source is then energizedso that laser energy travels through each of the optical fibers andsubstantially photoablates the plaque adjacent the second end of thecatheter body. The catheter body is then advanced through the region tophotoablate the plaque in such region.

[0006] A guide wire typically is required to properly position thecatheter in the artery. The guide wire is advanced through the arteryand region of plaque build-up so that it forms a path through the arteryand plaque build-up. The catheter is then guided through the arteryusing the guide wire.

[0007] One known catheter includes ultrasound sensors positioned at itsdistal end for displaying images of the artery while the catheter isadvanced. Known ultrasound sensors are coupled to an outer perimeter ofthe catheter and emit sound waves substantially radially from thecatheter distal end toward the artery wall. The sound waves then arereflected by the surrounding tissue, e.g., the artery wall and plaque,and toward the ultrasound sensors. The reflected sound waves are thencompared to the transmitted sound waves to generate an ultrasound imageof the tissue radially sounding the distal end.

[0008] To advance the catheter, an operator first positions the catheterat a first location in the artery. Sound waves are then emitted from andreceived by the ultrasound sensors, and an image is then displayedshowing the artery tissue adjacent the circumference of the catheter atsuch first location. The catheter is then advanced to a second locationin the artery, and a second image is displayed showing the artery atsuch location. This process is then continued until the catheter isadvanced through the artery and the plaque-build up.

[0009] Utilizing known ultrasound sensors as described above results indisplaying images of the portions of the arterial wall which areradially disposed about the catheter, but does not provide images of thearterial wall or plaque positioned immediately forward the catheter.Particularly, and because of the reflection of the sound waves, thesensors must be aligned within the artery so that the sound wavesprojected toward the artery wall are substantially perpendicular to theartery wall when reflected to the sensors. Sound waves that are notperpendicular to the artery wall may provide inaccurate signals, whichmay result in the display of inaccurate images, which is undesirable.

[0010] Inaccurate images may result in improperly guiding the catheterthrough the blood vessel, which is undesirable. Particularly, knowncatheters must be manually inserted and guided through the blood vessel.Typically, a surgeon or other operator utilizes the displayed images toguide the catheter through the vessel and avoid damaging healthy tissue,i.e., the artery wall. If an inaccurate image displays plaque eventhough such tissue actually is an artery wall, it is possible that theoperator may photoablate the artery wall, which is undesirable.

[0011] It would be desirable to provide a guidance system which providesimproved image accuracy as compared to known catheters. It also would bedesirable for such guidance system to be substantially easy to implementin connection with medical apparatus other than catheters. It furtherwould be desirable for such guidance system to facilitate automaticadvancement of the catheter through the body.

SUMMARY OF THE INVENTION

[0012] These and other objects are attained by a catheter which, in oneembodiment, includes a catheter body and at least one interferometricguidance system. The catheter body includes a bundle of optic fibers,each having a first end and a second end, and the second ends of therespective optic fibers form a substantially rounded catheter head.

[0013] Each interferometric guidance system is coupled to the catheterbody and includes a first optic fiber, a second optic fiber, and adetecting element. The first optic fiber of each guidance systemincludes a first end and a second end, and is coupled to the catheterbody so that the second end is adjacent the catheter head. The secondoptic fiber of each guidance system similarly includes a first end and asecond end, and a reference mirror is positioned adjacent the secondoptic fiber second end.

[0014] The detecting element of each guidance system is communicativelycoupled to both the first optic fiber and the second optic fiber of suchguidance system. Particularly, the first optic fiber first end iscommunicatively coupled to the detecting element and the second opticfiber first end is communicatively coupled to the detecting element. Thedetecting element is configured to determine interference betweensubstantially equal light beams which are emitted from the same sourceand which are split to propagate through the first optic fiber andthrough the second optic fiber. The interference is then utilized todetermine the density and type of tissue adjacent the catheter head, andto guide the catheter head through the tissue.

[0015] In operation, the catheter head is inserted at least partiallyinto a blood vessel so that the catheter head and the first optic fibersecond end of each guidance system is positioned in the blood vessel.The second optic fiber of each guidance system is positioned outside theblood vessel. The reference mirror of each guidance system is positioneda desired, or measuring, distance from its respective second optic fibersecond end. The distances between the respective reference mirrors andoptic fiber second ends may either be the same or different.

[0016] With respect to each detecting element, a light beam is splitinto first and second substantially equal light beams which are thentransmitted through the first and second optic fibers of each guidancesystem, from their respective first ends to their respective secondends. The first light beam transmitted through the first optic fiberexits from the first optic fiber second end, is at least partiallyreflected by the tissue, re-enters the first optic fiber second end andpropagates toward the first optic fiber first end. Similarly, the secondlight beam transmitted through the second optic fiber exits from thesecond optic fiber second end, is at least partially reflected by thereference mirror, re-enters the second optic fiber second end andpropagates toward the second optic fiber first end.

[0017] Each detecting element detects interference between therespective reflected first light beam and the reflected second lightbeam and transmits interference data to a computer. The computer thenutilizes the interference data to determine the density and the type ofthe tissue to be examined adjacent the catheter head. Particularly, theinterference data is representative of the density and type of tissuelocated at the measuring distance from the second optic fiber secondend, and the computer utilizes such data to generate an image of suchtissue at such location. The computer also utilizes the interferencedata to control subsequent advancement of the catheter through theartery.

[0018] The above described guidance systems facilitate obtaining moreaccurate images than obtained using ultrasound. In addition, suchsystems are believed to be substantially easy to implement in connectionwith medical apparatus other than catheters. Furthermore, such systemsare believed to facilitate automatic control and advancement of thecatheter through the body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a pictorial illustration of a catheter including twoguidance systems in accordance with one embodiment of the presentinvention inserted into a blood vessel.

[0020]FIG. 2 is a front cross section view of the catheter body shown inFIG. 1.

[0021]FIG. 3 is a schematic illustration of the catheter control elementshown in FIG. 1.

[0022]FIG. 4 is a schematic illustration of one of the guidance systemsshown in FIG. 1.

DETAILED DESCRIPTION

[0023]FIG. 1 is a pictorial illustration of a catheter assembly 20including two guidance systems 22A and 22B in accordance with oneembodiment of the present invention inserted into a blood vessel 24 of abody. Catheter assembly 20 includes a control element 26 and a catheterbody 28. Catheter body 28 has a first end 30 and a rounded, orhemispherical, second end, or head, 32, and includes a plurality ofoptic fibers (not shown in FIG. 1). Catheter body first end 30 iscommunicatively coupled to control element 26 and catheter body secondend 32 is positioned within an interior 34 of blood vessel 24 adjacenttissue to be imaged, e.g., plaque 36.

[0024] Each guidance system 22A and 22B includes a respective controlelement 40A and 40B, a respective first, or measuring, optic fiber 42Aand 42B, and a respective second, or reference, optic fiber 44A and 44B.First optic fibers 42A and 42B include respective first ends 46A and 46Band respective second ends 48A and 48B, and are coupled to catheter body28 so that second ends 48A and 48B are adjacent catheter head 32 and arepositioned in blood vessel interior 34. Second optic fibers 44A and 44Balso include respective first ends 50A and 50B and respective secondends 52A and 52B. First optic fiber first end 46A and second optic fiberfirst end 50A are communicatively coupled to system control element 40A,and first optic fiber first end 46B and second optic fiber first end 50Bare communicatively coupled to system control element 40B.

[0025] First system first optic fiber 42B is configured to emit energywaves substantially coaxially with respect to catheter head 32. Secondsystem first optic fiber 42B is configured to emit energy wavessubstantially radially with respect to catheter head 32. Particularly,second end 48B of optic fiber 42B includes a prism (not shown in FIG. 1)configured to emit an energy beam at an angle with respect to catheterhead 32, e.g., perpendicularly with respect to optic fiber 42A.

[0026] Each guidance system control element 40A and 40B includes arespective diagnostic light beam source 54A and 54B, a respective beamsplitter 56A and 56B, and a respective detecting element 58A and 58B.Beam splitters 56A and 56B are communicatively coupled to first opticfiber first ends 46A and 46B, respectively. Similarly, beam splitters56A and 56B are communicatively coupled to second optic fiber first ends50A and 50B, respectively. Beam splitters 56A and 56B also are coupledto respective diagnostic light beam sources 54A and 54B and detectingelements 58A and 58B via optic fibers 64A and 64B, respectively.

[0027] Detecting elements 58A and 58B are coupled to an image screen 38and are configured to transmit image data to image screen 38 fordisplaying an image of the tissue to be imaged. Detecting elements 58Aand 58B also are configured to transmit control data to catheter controlelement 26. Particularly, detecting element 58A is configured todetermine interference between a light beam propagating through firstoptic fiber 42A and a light beam propagating through second optic fiber44A, and to generate interference data representative of suchinterference. For example, detecting element 58A may include a detector,a demodulator and an analog digitizer which cooperate in a known mannerto generate such interference data. Such interference data istransmitted to a computer 66A, which generates image data for display onimage screen 38 and generates control data for transmission to cathetercontrol element 26. Similarly, detecting element 58B is configured todetermine interference between a light beam propagating through firstoptic fiber 42B and a light beam propagating through second optic fiber44B, and to generate interference data representative of suchinterference. Such interference data is transmitted to a computer 66B,which generates image data for display on image screen 38 and generatescontrol data for transmission to catheter control element 26.

[0028] Referring to FIG. 2, catheter body 28 includes several opticfibers 68 extending through a housing, or casing, 70. Second systemfirst optic fiber 42B is coupled to housing 70 so that housing 70extends between such second system first optic fiber 42B and catheterbody optic fibers 68. First system first optic fiber 42A extends throughand is substantially centered within housing 70. Alternatively, secondsystem first optic fiber 42B may be positioned within housing 70 andfirst system optic fiber 42A may be positioned outside housing 70. Ofcourse, both first system optic fibers 42A and 42B may be positionedeither within housing 70 or outside housing 70.

[0029] Referring now to FIG. 3, catheter control element 26 includes atherapeutic laser source 72 substantially aligned with catheter bodyoptic fibers 68. Laser source 70 is configured to transmit a therapeuticlaser beam through catheter body optic fibers 68 for photoablatingplaque 36 (FIG. 1), or other tissue.

[0030] Referring now to FIG. 4, guidance system 22A further includes areference mirror 74A positioned adjacent second fiber second end 52A.Reference mirror 74A is movable with respect to second fiber second end52A and is controlled, for example, by computer 66A. Similarly, whilenot shown in FIG. 4, guidance system 22B includes a reference mirror 74Bpositioned adjacent second fiber second end 52B. Reference mirror 74B ismovable with respect to second fiber second end 52B and is controlled,for example, by computer 66B.

[0031] Prior to inserting catheter assembly 20 into blood vessel 24,each guidance system 22A and 22B is calibrated. Particularly, referencemirror 74A is positioned a distance D₁ from second fiber second end 52Aand guidance system 22A is calibrated so that interference data obtainedby detecting element 58A is representative of tissue locatedapproximately the same distance D₁ from first optic fiber second end48A. Similarly, reference mirror 74A is positioned a distance D₂ fromsecond fiber second end 52B and guidance system 22B is calibrated sothat interference data obtained by detecting element 58B isrepresentative of tissue located approximately the same distance D₂ fromfirst optic fiber second end 48B.

[0032] Referring again to FIG. 1, and after calibrating guidance systems22A and 22B, catheter assembly 20 is inserted into blood vessel 24 sothat catheter head 32 and first optic fiber second ends 48A and 48B arepositioned within blood vessel 24, and second optic fiber second ends52A and 52B are positioned outside blood vessel 24, and outside thebody. First reference mirror 74A, as explained above, is positioneddistance D₁ from second optic fiber second end 52A, and second referencemirror 74B is positioned distance D₂ from second optic fiber second end52B.

[0033] Light beam source 54A transmits a diagnostic light beam to beamsplitter 56A, which splits the light beam into first and secondsubstantially equal light beams 76A and 78A, respectively. First lightbeam 76A is then transmitted through first optic fiber 42A and secondlight beam 78A is transmitted through second optic fiber 44A. Firstlight beam 76A exits from first optic fiber second end 48A substantiallycoaxially with respect to catheter head 32, is at least partiallyreflected by the tissue, re-enters first optic fiber second end 48A andpropagates toward first optic fiber first end 46A. Similarly, secondlight beam 78A transmitted through second optic fiber 44A exits fromsecond optic fiber second end 52A, is at least partially reflected byreference mirror 74A, re-enters second optic fiber second end 52A andpropagates toward second optic fiber first end 50A.

[0034] Detecting element 58A detects light interference patterns, e.g.,interferences, between the reflected first light beam 76A and reflectedsecond light beam 78A, and transmits interference data representative ofsuch interferences to computer 66A. Computer 66A utilizes theinterference data to determine the type and depth of the tissue locatedat a distance D₃ from first optic fiber second end 48A. Particularly,computer 66A utilizes the interference data to determine what type oftissue, if any, is located at a distance D₃ from first fiber second end48A, where distance D₃ is substantially the same as distance D₁. Forexample, computer 66A may include a memory, and representativeinterference signals for different types of tissues, e.g., plaque,artery walls, healthy tissue, cancerous tissue, may be stored in suchmemory. Computer 66A compares the interference data received fromdetecting element 58A to such stored representative interference signalsto determine the type of tissue located distance D₃ from first fibersecond end 48A. Distances D₁ and D₃ may, for example, be less than orequal to 1 millimeter, e.g., one quarter of a millimeter. Of course,distances D₁ and D₃ may be larger than 1 millimeter.

[0035] If desired, reference mirror 74A may be moved with respect tosecond fiber second end 48A to recalibrate guidance system 22A while itis positioned in a blood vessel 24. Particularly, if detecting element58A generates interference data representative of a loss of signalthrough first optic fiber 42A, reference mirror 74A may be moved toreestablish a signal at a distance D₄ (not shown in FIG. 1) which isdifferent from distance D₁.

[0036] Similarly, and in yet another alternative, reference mirror 74Amay be moved with respect to second fiber second end 48A to determinethe type and depth of the tissue located at a varying distances fromsecond fiber second end 48A. Particularly, reference mirror 74 may bemoved between a point immediately adjacent second fiber second end 48Aand a point distance D₁ from second fiber second end 48A to determinethe type and depth of the tissue located at each point between such twopoints. Accordingly, reference mirror 74A may be moved to determinetissue type at multiple different distances from second fiber second end48A.

[0037] Computer 66A generates image data of such tissue and displays theimage of such tissue on image screen 38. Particularly, computer 66Autilizes the interference data generated at various points in the tissueto generate image data representative of a substantially linear imageprofile of the examined tissue. Computer 66A also utilizes theinterference data to generate and transmit control signals to cathetercontrol element 26, as is described in more detail below.

[0038] Similarly, light beam source 54B transmits a diagnostic lightbeam to beam splitter 56B, which splits the light beam into first andsecond substantially equal light beams 76B and 78B, respectively. Firstlight beam 76B is then transmitted through first optic fiber 42B andsecond light beam 78B is transmitted through second optic fiber 44B.First light beam 76B exits from first optic fiber second end 48Bsubstantially radially with respect to catheter head 32, is at leastpartially reflected by the tissue, re-enters first optic fiber secondend 48B and propagates toward first optic fiber first end 46B.Similarly, second light beam 78B transmitted through second optic fiber44B exits from second optic fiber second end 52B, is at least partiallyreflected by reference mirror 74B, re-enters second optic fiber secondend 52B and propagates toward second optic fiber first end 50B.

[0039] Detecting element 58B detects interference between the reflectedfirst light beam 76B and reflected second light beam 78B, and transmitsinterference data representative of such interference to computer 66B.Computer 66B utilizes the interference data, as described above, todetermine the type of tissue located a distance D₅ between the tissueand first optic fiber second end 48B, where distance D₅ is substantiallythe same as distance D₂. Computer 66B, utilizing the interference data,generates image data of such tissue, as described above, and displaysthe image on image screen 38. Computer 66B also utilizes theinterference data to generate and transmit control signals to cathetercontrol element 26, as is described in more detail below.

[0040] If the tissue located at distance D₃ and D₅ is, for example,plaque 36, then catheter assembly 20 may be utilized to photoablateplaque 36. Particularly, computers 66A and 66B may transmit controlsignals to control element 26 so that control element 26 energizes lasersource 72 to transmit a laser beam through catheter body optic fibers68. The laser beam propagates through catheter body optic fibers 68 andphotoablates the plaque 36 in a known manner.

[0041] Alternatively, computers 66A and 66B may transmit control signalsto control element 26 so that control element 26 energizes laser source72 to transmit a laser beam through only selected catheter body opticfibers 68. For example, if interference data obtained at first systemdetecting element 58A indicates that the tissue in front of catheterhead 32 is plaque 36, and if second system detecting element 58Bindicates that the tissue adjacent second system first optic fiber 42Bis an artery wall, then control element may transmit a laser beam onlythrough optic fibers 68 adjacent first system first optic fiber 42B, andnot through optic fibers 68 adjacent second system first optic fiber42A.

[0042] To facilitate determining accurate tissue depth and tissue typeduring blood vessel 24 movement, e.g., if blood vessel 24 is located inthe heart, where blood vessel 24 may move relative to catheter head 32even if catheter head 32 is not advanced through blood vessel 24,guidance systems 22A and 22B may be configured to determine tissue typeand density at only periodic intervals. For example, if blood vessel 24is located in the heart, and it is not practical to stop the heart, thencomputers 66A and 66B may be configured to sample interference data fromrespective detecting elements 58A and 58B at a same period of time ofthe cardiac cycle. Particularly, computers 66A and 66B may becommunicatively coupled to an EKG and configured to sample interferencedata only at the top of the R wave. Alternatively, computers 66A and 66Bmay be communicatively coupled to an EKG and configured to sampleinterference data only at the middle of the T wave. Of course, computers66A and 66B may be configured to sample interference data at otherperiodic intervals.

[0043] The above described catheter and guidance systems facilitateobtaining higher resolution images than obtained using ultrasound. Suchguidance systems also are believed to be substantially easy to fabricateand utilize in connection with a catheter such as catheter assembly 20.

[0044] In an alternative embodiment, the second optic fiber second endprism may be configured to emit first light beam 76B angularly withrespect to an axis of first optic fiber 42B but not perpendicularly withrespect to such axis. Accordingly, images may be obtained of tissueabout a circumference of catheter head 32, rather than merely the tissuepositioned coaxially with catheter head 32 or radially with respect tocatheter head 32.

[0045] In addition, and in accordance with yet another embodiment of thepresent invention, a catheter may be utilized in connection withseveral, e.g., five, guidance systems 22. The guidance systems 22 may bepositioned so that respective measuring, or first optic fibers, arepositioned to emit light beams coaxially with respect to the catheterhead, as well as substantially about the entire circumference of thecatheter head.

[0046] In still yet another embodiment of the present invention,measuring fibers 42A and 42B are configured to transmit both diagnosticlight beams from respective diagnostic light beam sources 54A and 54Band therapeutic laser beams from therapeutic laser source 72.Particularly, measuring fiber 42A is communicatively coupled to bothlight beam source 54A and laser source 72. Similarly, measuring fiber42B is communicatively coupled to both light beam source 54B and lasersource 72. Laser source 72 and light beam sources 54A and 54B may beconfigured to transmits beams having different wave lengths tofacilitate simultaneous transmission of both the therapeutic laser beamand diagnostic light beams through measuring fibers 42A and 42B.

[0047] Guidance systems 22A and 22B may also be implemented inconnection with medical apparatus other than catheters. For example,guidance systems 22A and 22B may be coupled to a medical apparatus suchas an angioplasty balloon or an atherectomy device. Similarly, guidancesystems 22A and 22B may be utilized in connection with hollow tubesconfigured to facilitate localized treatment. For example, guidancesystems 22A and 22B may be utilized to position a hollow tube adjacent aregion so that medicine, radiation, or energy may be transmitteddirectly to such region. Similarly, guidance systems 22A and 22B may beutilized to facilitate positioning biopsy devices proximate desiredsites.

[0048] Guidance systems 22A and 22B also facilitate automatic control ofthe advancement of catheter assembly 20 through blood vessel 24.Particularly, and in accordance with still yet another embodiment,guidance systems 22A and 22B are coupled to a motor (not shown) which iscoupled to catheter body 28. The motor is configured to advance catheterbody 28 through the body and to receive control signals from respectivecomputers 66A and 66B. If respective computers 66A and 66B transmitcontrol signals indicating that the tissue adjacent catheter head 32 is,for example, plaque, then the motor advances catheter head 32 throughthe plaque. If, however, computers 66A and 66B transmit control signalsindicating that the tissue adjacent catheter head 32 is, for example, anormal artery wall, then the motor stops advancing catheter head 32.

[0049] From the preceding description of the present invention, it isevident that the objects of the invention are attained. Although theinvention has been described and illustrated in detail, it is to beclearly understood that the same is intended by way of illustration andexample only and is not be taken by way of limitation. For example,while the guidance system was described in connection with a catheterhaving a rounded head, such system may be utilized in connection with acatheter having a different shaped, e.g., a spherical, or an angular,head. In addition, while the guidance systems included diagnostic lightsources configured to emit a light beam, such light sources may beconfigured to emit any coherent light beam, such as laser light orpolarized light. Furthermore, while each guidance system was describedin connection with its own computer, the guidance systems may be coupledto one computer. Accordingly, the spirit and scope of the invention areto be limited only by the terms of the claims.

What is claimed is:
 1. A method for guiding a medical instrument througha blood vessel, said method comprising the steps of: inserting themedical instrument at least partially into the blood vessel; utilizinglaser interferometry to guide the medical instrument through the bloodvessel.
 2. A method in accordance with claim 1 wherein the medicalinstrument is a catheter having a catheter head, and wherein insertingthe medical instrument at least partially into the blood vesselcomprising the step of inserting the catheter head into the bloodvessel.
 3. A method in accordance with claim 1 wherein utilizing laserinterferometry to guide the medical instrument through the blood vesselcomprises the step of coupling at least one guidance system to themedical instrument, the guidance system including a first optic fiberhaving a first end and a second end, a second optic fiber having a firstend and a second end, a reference mirror positioned adjacent the secondoptic fiber second end, and a detecting element communicatively coupledto the first ends of said first and second optic fibers, the detectingelement configured to determine interference between a light beampropagating through the first optic fiber and a light beam propagatingthrough the second optic fiber.
 4. A method in accordance with claim 3wherein coupling at least one guidance system to the medical instrumentcomprises the step of coupling at least two guidance systems to themedical instrument.
 5. A method in accordance with claim 3 whereincoupling at least one guidance system to the medical instrumentcomprises the step of coupling five guidance systems to the medicalinstrument.
 6. A method in accordance with claim 3 wherein the medicalinstrument is a catheter.
 7. A method in accordance with claim 3 whereinthe medical instrument is an angioplasty balloon.
 8. A method inaccordance with claim 3 wherein the medical instrument is an atherectomydevice.
 9. A method in accordance with claim 3 wherein the medicalinstrument is a biopsy device.
 10. A method in accordance with claim 3wherein the medical instrument is a hollow tube.
 11. A method inaccordance with claim 1 wherein utilizing laser interferometry to guidethe medical instrument through the blood vessel comprises the step ofgenerating an image of tissue adjacent the medical instrument.
 12. Amethod in accordance with claim 11 wherein said image is a linearprofile image of the tissue adjacent the medical instrument.
 13. Amethod in accordance with claim 11 comprising the step of generating animage of tissue coaxially aligned with the medical instrument.
 14. Amethod in accordance with claim 1 wherein utilizing laser interferometryto guide the medical instrument through the blood vessel comprises thestep of automatically controlling the medical instrument.
 15. A methodin accordance with claim 1 further comprising the step of utilizingultrasound for imaging at least portions of the blood vessel.
 16. Amedical system configured to be guided through body tissue, said medicalsystem comprising: a medical instrument having a first end and a secondend; a first guidance system comprising a first optic fiber having afirst end and a second end, a second optic fiber having a first end anda second end, a reference mirror positioned adjacent said second opticfiber second end, and a detecting element communicatively coupled tosaid first ends of said first and second optic fibers, said first opticfiber coupled to said medical instrument so that said second end of saidfirst optic fiber is adjacent said second end of said medicalinstrument, said detecting element configured to determine interferencebetween a light beam propagating through said first optic fiber and alight beam propagating through said second optic fiber; and a secondguidance system comprising a first optic fiber having a first end and asecond end, a second optic fiber having a first end and a second end, areference mirror positioned adjacent said second optic fiber second end,and a detecting element communicatively coupled to said first ends ofsaid first and second optic fibers, said first optic fiber coupled tosaid medical instrument so that said second end of said first opticfiber is adjacent said second end of said medical instrument, saiddetecting element configured to determine interference between a lightbeam propagating through said first optic fiber and a light beampropagating through said second optic fiber.
 17. A medical system inaccordance with claim 16 wherein said medical instrument is anatherectomy device.
 18. A medical system in accordance with claim 16wherein said medical instrument is an angioplasty balloon.
 19. A medicalsystem in accordance with claim 16 wherein said medical instrument is acatheter.
 20. A system in accordance with claim 18 wherein said catheteris a laser catheter.
 21. A medical system in accordance with claim 20wherein said laser catheter comprises a plurality of optic fibers, oneof said plurality of fibers comprising said first guidance system firstoptic fiber.
 22. A medical system in accordance with claim 21 whereinsaid first guidance system first optic fiber is communicatively coupledwith both a diagnostic energy source and a therapeutic energy source,said diagnostic energy source configured to emit an energy beam having adifferent wavelength than an energy beam emitted by said therapeuticenergy source.
 23. A medical system in accordance with claim 16 whereinsaid medical instrument is a biopsy device.
 24. A medical system inaccordance with claim 16 wherein said medical instrument is a hollowtube.
 25. A medical system in accordance with claim 16 furthercomprising at least one additional guidance system.
 26. A medical systemin accordance with claim 16 wherein at least one of said first andsecond guidance systems is configured to determine a distance betweensaid second end of said respective first optic fiber and an artery wall.27. A medical system in accordance with claim 16 wherein at least one ofsaid first and second guidance systems is configured to determine a typeof tissue positioned a distance from said second end of said respectivefirst optic fiber.
 28. A medical system in accordance with claim 16wherein at least one of said first and second guidance systems iscoupled to a motor, said motor coupled to said medical instrument, andwherein said guidance system and said motor are configured to cooperateand automatically control advancement of said medical instrument throughthe body tissue.
 29. A medical system in accordance with claim 16wherein at least one of said first and second guidance systems isconfigured to determine a type and density of tissue adjacent saidmedical instrument at periodic intervals.